Hi @mark. The problem is that Bubble only loads data when it displays it. So, you are not preloading anything really as you may think, because all you groups are hidden.
The (interim) solution I have found for myself is not to hide the groups, but to make them invisible with CSS (using Toolbox plugin). Put all your RGs into a floating group which is visible on page load, and add style to visibility:hidden. This way, data will be loaded and displayed, but will not be seen by users.
You need floating groups because visibility actually preserves the element space, just making it invisible.
When you have your data preloaded this way, it is cached by the browser, so whenever you display it anywhere else in your app (outside of invisible hidden groups) - it shows up immediately.